Thermally responsive switch



zvsheetg-shetvl mum Aug.. 13, 1963 l Filed Jung 5. 1960 Allg- 13', 1963 I GRlMsHAw 3,100,827 THERMALLY ARESPONSIVE SWITCH Filed June 5, 1960 2 Sheets-Sheet 2 p .3,100,32'1:A THERMALLY nnsPoNsivn swrrcn Charles Grimshaw, Fulton, lll., assignor to General Electric Company, a corporationof New York` Filed June 3, 1960, Ser. No. 33,817 3 Claims. (Cl. 20D-113) This invention relates to thermally responsive switches, and more particularly, thermally responsive overload switches of the automatically resetting type.

vThermally responsive overload switches are frequently used to provide thermal protection for electrical apparatus, such as electric motors. One form of such a switch incorporates a bimetallic element carrying the movable contact,l and a stationary contact which cooperates with the movable contact to control the circuit of the apparatus to be protected. The bimetallic element and the stationary contact of such a switch may be `serially connected in the circuit to be protected, and the switch may be made responsive to both the ambient temperature and overload current. In order to provide an eiiicient'protective switch for an electric motor, it is often advantageous to mount.

3,l@0,327 Patented Aug. 13, 1963 tion when taken in conjunction with the accompanyingswitch embodying my invention;`

such a switch in a relatively small area, such as directly Within or between the windings ofthe motor, so that the switch will respond -directly to the ambient temperature of the windings. For this application, it is desirable that such a switch have a housingof high thermal conductivity and of extremely low thermal mass, and also that it substantially reduce the amount of internal heating for the switch so that it will provide an eicient temperature i tured at a reduce-d cost.

Another object of this invention r'is to provide a new and improved thermally responsive switch which includes a novel switch housing of extremely thin or flat over-all conguration and has an extremely low thermal mass, with high thermal conductivity. V

A further object of this invention is toprovide anew and improved thermally responsive switch of wafer-like congurationwhich may be conveniently mounted in relatively small positions in an electrical apparatus for efficiently sensing ambient temperature. and providing overload protection.

In carrying out my invention, in one -form thereof, I apply it to a thermally responsive switch having a pair of contacts and a thermally responsive bimetallic member; The switch housing is formed by the cooperation of a pair of thin conductive strips at least one'of which is recessed. The bimetallic member is attached to one of these conductive strips and its free end carriesa movable contact. A-fixed contact which mates with the movable contact is attached to the inner surface of the other strip. Each of the recessed strips has a terminal portion integral to it. Between the two strips, an insulatingspacer is inter- PIG. 2 is a plan view of the switch of FIG. 1, with a portion of the upper strip of the switch housing broken away to show part of the bimetal and the movable contact which it` carries; p

FIG. 3 is 4a sectional view taken substantially along the line A-A of FIG. 2;

FIG. 4 is a sectional view taken substantially along the line B-B of FIG. l, with the insulating spacer represented by dotted lines;

FIG. 5 is a perspective View of the switch of FIG. 1, partially exploded to show interior details;

FIG. 6` is a perspective view of the switch of FIG. 1; and

FIG. 7 is a schematic sectional View of a portion of a motor incorporating the thermally responsive switch of' the present invention. n

vReferring now to the drawings, and more particularly to FIGS. 3 and 5, I have shown a thermally responsive switch 1 which. consists of only a few basic parts, and includes an upper conductive sub-assembly, a lower conductive sub-assembly, and an intermediate insulating spacer means.

To substantially reduce the thickness of `switch 1 and give it a diminutive, and wafer-like or pill-shaped over-all appearance, housing 3 of myswitch 1 has been made from a pair of thin recessed metallic strips 5 and7. One of these strips, such as upper stript 5, has a recessed portion ror cavity 9 for receiving the bimetallic movable arm 11 of the switch. (See FIG. 3.) A stepped surface section 13 is formed in one side of the peripheral flange 35 surrounding the cavity 9 (as shown in FIG. 5), and support 15 for the bimetallic contact arm 11 is fastened to this section 13 by welding. For connecting strip S to the bared end of a conductor lead, outwardly extending tab 17 has Ibeen formed thereon. Tab 17 may be crimped and welded (as seen in FIG. 2) to one or more of the conductor leads of the control circuit for an electrical apparatus such as a motor which is to be protected from thermal overload. Tab 17 thus serves as an integral external terminal for conductive strip 5 so that an effective terminal area of low electrical resistance is thereby obtained. The thin thermally conductive area of strip 5 also provides a low thermal mass for sensing ambient temperatures of an external apparatus.

Turning now to the thermally responsive means affixed tostrip 5, this comprises the bimetallic contact arm illustrated at 11. The construction and arrangement of the particular arrn 11 illustrated herein, together with the method of manufacturing it, `is the invention of John L. Slonneger, `and this construction and arrangement are described in detail and claimed in his copending-application Serial No. 1l,7l8,'f1led on February 29, 1960, and assigned to the same assignee as the present invention. Bimetallic arm V11 (as shown in FIG. 4) is essentially a split annular disc of bimetallic material. This bimetal disc includes a pair of arcuate arms 23 with their free ends 21 separated by a radially extending .gap or split. The disc or arm 11 is attached to support 15, as shown in FIGS. 4 land 5, by welding a base portion of the disc. (opposite to the free lends thereof) to anintennrediate section of the `support 15 so that the free ends of the bimetaly are suspended from the support in cantilever fashion. The free ends of the bimetal are then drawn tobest be understood by reference to the following descripward each other to reduce the gap the desired amount and theV disc is Stressed into a dished formation. Contact lbutton 19 is then welded to the free ends of the bimetal to retain them in their drawn position, and the size of the gap between fthe free ends of the ibimetal determines the A desired level ofternperature response.

As seen in FIG. 5, upper strip of my switch 1 thus has l the thermally responsive snap Vacting vbimetal arm 11 mounted upon it by means of support 15, so that an electric current path of low electrical resistance and very low thermal mass is provided from tab terminal 17 to the contact button 19 through the -thermally and electrically conductive strip 5, lthe support 15, and bimetal 11. All of these aforementioned elements which are attached tc upper strip 5 make up the upper strip sub-assembly, as shown in FIG. 5.

. Turning now tothe lower conductive sub-assembly of my switch 1, as shown at the bottom of FIG. y5, lower strip 7 is somewhat similar in overall appearance to upper strip 5, and is both thermally and electrically conductive.

` Strip 7 includes recessed portion 25 which has essentially the same area as recess 9, and it also has an outwardly extending tab 27 for crimping and welding one or more other control circuit conductor leads thereto for connection to the other side orf the 'control cinouit. (See FIG. 2). Fixed contact button 33 is welded to the inner surface of recess 25. Button 33 extends upwardly from the inner surface of strip 7 (as shown in FIG. 5) to mate with movable contact button 19 upon flexure of bimetallic yarm 11 to its contacts closed position.

As seen in FIG. 5, lower strip 7 thus comprises an electrically conductive path between terminal tab 27 thereof and xed contact button 33 through strip 7. These elel ments make up the lower conductive sub-assembly, and

this sub-assembly also has a low electrical resistance land a very low thermal mass.

The upper and lower conductive sub-assemblies are fastened together in a sim-ple and eliicient manner to form my switch 1. For this purpose, strip 7 has a plurality of 4longitudinally spaced peripheral tabs 29 integral thereto. To electrically insulate the conductive paths formed by the uppervand lower conductive sub-assemblies of which strips 5 and 7 are a part, I haveprovided a specially constructed slotted insulating spacer 31. (See FIG. 5.) The periphery of this spacer extends beyond the oppositely disposed outer edges of strips 5 land 7 (as shown by FIGS. 4 and 6), and it also has extensions or flaps 31a and 31C which protrude further outwardly adjacent tabs 29. To yfasten the two sub-assembli-es together,

the thin spacer 31 is iirst interposed between them in the manner suggested by FIG'. 4. The tabs 29 of strip 7 are then bent over and against the upper surface of the peripheralflange 35 which surrounds recess 9 of strip 5, to securely fasten the two strips together. Spacer 31 is thus positioned in sandwich-like fashion between the two mating strips of switch housing 3. The ilaps 31a and 31C of spacer 31 adjacent tabs 29 are 'wrapped -around the flange 35 of strip 5 with the tabs and held firm-ly against the flange 35 underneath the tabsv (as shown in FIG; 6) to assure the proper insulation -between the strips.

To conveniently :calibrate my assembled switch 1 for the desired trip temperature, or the temperature at which the bim'etallic movable contact larm 11 snaps open, I have provided calibration screw 37. Screw 37 has a small outwardly convex head portion, and a shank portion 41 which `is in threaded engagement with a tapped hole 43 in strip 5.V Hole 43 overlies cantilevered extension 15a of bimetal support 15. As screw 37 is tightened, its threaded engage-ment with tapped hole 43 of strip 5 forces it inwardly into the recessed portion 9 of the housing 3 to thus deflect extension 15a of support 15 downwardly (as f plied by the snap acting bimetal arm 11 following engagement of movable contact button 19 with fixed contact button 33 and thus lowers the trippingtemperature. Conversrely, by loosening or unscrewing the calibration screw 37 from its tapped hole, extension 15a is deflected away from strip 7 to increasethe contact pressure and raise the tripping temperatureof the switch.

To insure against the possibility of extension 15a of the bimetal support engaging the bottom of strip 7 and thus short circuiting the switch contacts, spacer 31 has an inner extension 31134 which lies directly between extension 15a and strip 7 to provide insulation therebetween.' (See FIGS\.4and5.)QA .W

In order t0 reduce the over-all dimensions of my switch 1 and thus enhance its versatility, the upper and lower strips 5 and 7 are each stamped from a relatively thin sheet of metallicmaterial, `such as sheet steel having a thickness of .025 inch. The depth of the strips` 5 and 7 after their recesses have been stamped therein may be in the order of lessV than 3/32' of an inch. Housing 3 of the completely assembled switch 1 thus has the appearance of a wafer-thin or pill-shaped watchca'se having a deepnes's of less than 5%6 of an inch. y

In FIG. 7, I have illustrated my improved thermally responsive switch 1 as it might be positioned between the main and start windings 45 and 47 of a motor which it is to protect yfrom thermal overload. configuration allows it to fit in between the curvature of these windings, and the start winding 47 replaces the function of the conventional bimetal heater. Conductivestrips 5 and 7 provide a low resistance path for the flow of cur- .rent through the switch, whereby there is very little internal heating of the strips and the switch by the current passing therethrough. The placement of the motor protector .in the motor'may be part ofthe manufacturing process of the motor itself.

It will thus be seen that I have provided a diminutive, Wafer-thin, compact switch which includes a very simple conductive pair of strips that form a switch housing having integral terminations and a very low thermal mass with high thermal conductivity. This switch has a very low internal heating characteristic and will provide a good temperature response under load conditions. Besides providing very low electrical resistance, the strips 5 and 7 also result in 4a switch of low thermal mass. Thus as heat is supplied to the switch from the external apparatus to be controlled, for example, the switch 1 will follow closely the ambient temperature of its environment in that apparatus. Such a switch is simple and relatively easy to manufacture, and Vas a consequenceV thereof may be produced inexpensively. The over-all flat shape of this switch lends itself to numerous applications where the :size of the switch is an irnporant consideration. For any of its applications, my pill-shaped switch, will, of course, be electrically insulated from its patricular environment, and inthe motor shown in FIG. 7, it is insulated from the windings by the insulation of therrwindings themselves and also by an insulating layery or casing of plastic 49 formed abound the conductive housing. lIt will be obvious to those skilled in the art that, any number of simple techniques for electrically insulating my switch may be used, while in no way substantially increasing the over-all skilled in Ithe art that various changes and modifications may be made therein, without departing from my invention, and I therefore, aim in the following claims to cover Its wafer-like ,by-a pair of relatively thin conductive strips, said strips each having a recess therein :thereby to form a switch cavity, fixed contact 'Lrneans positioned on :the 4inner surface of one of said strips within said cavity, a support secured to said Vhousing betwween said s-trips and extending into said switch cavity, asnap acting disc supported in cantilever fashion by said support between a free inner end of said support and said housing and disposed in said cavity, said disc having a substantially annular configuration and constructed of bimetallic material, a movable ContactV means positioned on a free peripheral portion of said annular birnetal disc for cooperation with said fixed contact means, a screw in threaded engagement with one of said strips, extending through said annular Vrupted flange formed on the outer periphery thereof, said clamping tabs of the one strip being folded over against the flange of the other strip with doubled over folds of disc, and 'acting upon the free inner end of said support for selectively varying a predeterminable temperature atl which said disc will actuate said switch contacts, first insulating means electrically separating said strips from each other, said first insulating means comprising a thin layer of bendable insulating material, a plurality of clamping tabs formed on the outer periphery of one of. said strips, the other strip having a generally uninterrupted flange formed on the outer periphery thereof, said clamping tabs of the one strip being folded over against the flange of the other stripwith doubled over folds Aof the bendable insulating material interposed between` and clamped by the tabsof the one strip and the flange of the other strip, said strips being securely sandwiched together about said insulating layer by engagement of said tabs of said one strip with said flange of said'other strip, Vthereby to form a wafer-thin switch of compact configuration, low thermal mass, and high thermal conductivity, and a second insulating means substantially surrounding `the switch housing to insulateV the switch from its iexternal environment. t y

2. A thermally responsive snap acting electric switch comprising a housing of wafer-like configuration formed y by a pair of relatively thin conductive strips, said strips each having `a recess therein thereby to form a switch Vcavity, kfixed 'contact Ymeans positioned on the innery surface of one of said strips within saidcavity, an elongated support securedyat one end thereof'to said housing between strips and having a free inner end disposed in c said switch cavity, asnap acting -anuular disc of birnetal-` lic material supported in cantilever fashion within said switch cavity by Aattachment to said support betweeny the' ends thereof, a movable -contact button positioned on a free peripheral portion of said annular birnetal disc for cooperation with said fixed contact means, a screw in threaded engagement with one of said strips, extending through said vannular disc, and actingv upon said free inner end of said support ifor calibrating the temperature Y at which said disc will actuate said switch contacts, first insulating means electrically separating said strips from each other, said rst insulating means comprising a thin layer of bendable insulating material, a plurality of clamping tabs formed 4on the outer periphery of one of Said strips, the other strip having a generally uninterv'by a pair of relatively thin conductive strips, sai-d strips each :having a recess therein thereby to form a switch cavity, each of said strips having a terminal portion integral thereto, fixed contact means positioned on the inner surface of one of said strips within said cavity, an elongated support of rigid material'secured at one of its ends to said housing lbetween saidstrips and having an inner free end disposed in the approximate center of said switch cavity, a snap acting annular disc'of bimetallic material supported in cantilever` fashion within said switch cavity by attachment to said support between the ends thereof, a mov-able contact button positioned on a free peripheral portion of said annular birnetal disc for cooperation with said rfixed contact means, a screw in threaded engagement with one of said strips, extending through said annular disc, and -acting upon said free inner end of said support for moving said disc and selectively varying a predeterminable temperature at which said disc will actuate said switch contacts, first insulating means electrically sepa.-

. from the outer periphery of one of said strips, the other strip having ya generally uninterrupted Iflange formed on the outer periphery thereof, said clamping tabs of the one strip being vfolded over against the flange of the other strip with doubled overfolds of the ben-dable insulating material interposed Ibetween and clamped by the folded over tabs of the one strip and the flange of the other strip, said strips being securely sandwiched together about said insulating layer by engagement of said tabs of said one strip with said flange of said other strip, thereby to-.form a wafer-thin switch of compact configuration, low thermal mass, and high thermal conductivity, and a second insulating means substantially surrounding the switch housing to insulate the switch from its external environment.

References Cited in the file of this patent UNITED STATES PATENTS Italy a July 2, 

1. A THERMALLY RESPONSIVE SNAP ACTING ELECTRIC SWITCH COMPRISING A HOUSING OF WAFER-LIKE CONFIGURATION FORMED BY A PAIR OF RELATIVELY THIN CONDUCTIVE STRIPS, SAID STRIPS EACH HAVING A RECESS THEREIN THEREBY TO FORM A SWITCH CAVITY, FIXED CONTACT MEANS POSITIONED ON THE INNER SURFACE OF ONE OF SAID STRIPS WITHIN SAID CAVITY, A SUPPORT SECURED TO SAID HOUSING BETWEEN SAID STRIPS AND EXTENDING INTO SAID SWITCH CAVITY, A SNAP ACTING DISC SUPPORTED IN CANTILEVER FASHION BY SAID SUPPORT BETWEEN A FREE INNER END OF SAID SUPPORT AND SAID HOUSING AND DISPOSED IN SAID CAVITY, SAID DISC HAVING A SUBSTANTIALLY ANNULAR CONFIGURATION AND CONSTRUCTED OF BIMETALLIC MATERIAL, A MOVABLE CONTACT MEANS POSITIONED ON A FREE PERIPHERAL PORTION OF SAID ANNULAR BIMETAL DISC FOR COOPERATION WITH SAID FIXED CONTACT MEANS, A SCREW IN THREADED ENGAGEMENT WITH ONE OF SAID STRIPS, EXTENDING THROUGH SAID ANNULAR DISC, AND ACTING UPON THE FREE INNER END OF SAID SUPPORT FOR SELECTIVELY VARYING A PREDETERMINABLE TEMPERATURE AT WHICH SAID DISC WILL ACTUATE SAID SWITCH CONTACTS, FIRST 